scholarly journals Controlling the porosity of 316L stainless steel parts manufactured via the powder bed fusion process

2019 ◽  
Vol 25 (1) ◽  
pp. 162-175 ◽  
Author(s):  
Abdullah AlFaify ◽  
James Hughes ◽  
Keith Ridgway
Keyword(s):  
Stainless Steel ◽  
Layer Thickness ◽  
Exposure Time ◽  
Process Parameters ◽  
Pulsed Laser ◽  
Powder Bed Fusion ◽  
Content Type ◽  
Powder Bed ◽  
Point Distance ◽  
Part Density

Purpose The pulsed-laser powder bed fusion (PBF) process is an additive manufacturing technology that uses a laser with pulsed beam to melt metal powder. In this case, stainless steel SS316L alloy is used to produce complex components. To produce components with acceptable mechanical performance requires a comprehensive understanding of process parameters and their interactions. This study aims to understand the influence of process parameters on reducing porosity and increasing part density. Design/methodology/approach The response surface method (RSM) is used to investigate the impact of changing critical parameters on the density of parts manufactured. Parameters considered include: point distance, exposure time, hatching distance and layer thickness. Part density was used to identify the most statistically significant parameters, before each parameter was analysed individually. Findings A clear correlation between the number and shape of pores and the process parameters was identified. Point distance, exposure time and layer thickness were found to significantly affect part density. The interaction between these parameters also critically affected the development of porosity. Finally, a regression model was developed and verified experimentally and used to accurately predict part density. Research limitations/implications The study considered a range of selected parameters relevant to the SS316L alloy. These parameters need to be modified for other alloys according to their physical properties. Originality/value This study is believed to be the first systematic attempt to use RSM for the design of experiments (DOE) to investigate the effect of process parameters of the pulsed-laser PBF process on the density of the SS316L alloy components.

Powder characterization and part density for powder bed fusion of 17-4 PH stainless steel

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Sean Daniel Dobson ◽  
Thomas Louis Starr
Keyword(s):  
Particle Size ◽  
Stainless Steel ◽  
Flow Behavior ◽  
Full Density ◽  
Powder Bed Fusion ◽  
Metal Powders ◽  
Production Environment ◽  
Content Type ◽  
Powder Bed ◽  
Part Density

Purpose Characteristics of the metal powder are a key factor in the success of powder bed fusion (PBF) additive manufacturing. Powders for PBF from different manufacturers may have a different particle size and/or bulk packing and flow behavior. Powder properties change as the powder is reused for multiple builds. This study seeks to measure the variability of commercial 17-4 PH stainless steel powders to determine the effect of powder variability on part density and demonstrate characterization methods that ensure part quality. Design/methodology/approach Commercial atomized metal powders from four different vendors were produced with two different atomizing gases (N2 and argon). Powder was characterized in both new and extensively reused conditions. All powders were characterized for flow and packing behavior, particle size and internal porosity. Coupons were manufactured using the laser PBF process with optimized scan strategy and exposure parameters. The quality of fabricated parts was measured using bulk density measurement. Findings Despite differences in powder flowability and particle size, fully dense parts (>99 per cent) were produced using all powders, except one. Residual porosity in these parts appeared to result from gas trapped in the powder particles. The powder with extensive reuse (400+ h in machine fabrication environment) exhibited reduced flowability and increased fraction of fine particles, but still produced full density parts. Originality/value This study demonstrates that full density parts can be fabricated using powders with a range of flowability and packing behavior. This suggests that a single flowability measurement may be sufficient for quality assurance in a production environment.

Effects of layer thickness in laser-powder bed fusion of 420 stainless steel

2020 ◽  
Vol 26 (7) ◽  
pp. 1197-1208
Author(s):  
Subrata Deb Nath ◽  
Gautam Gupta ◽  
Martin Kearns ◽  
Ozkan Gulsoy ◽  
Sundar V. Atre
Keyword(s):  
Tensile Strength ◽  
Stainless Steel ◽  
Layer Thickness ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Corrosion Properties ◽  
Content Type ◽  
Powder Bed ◽  
Heat Treated ◽  
Mechanical And Corrosion Properties

Purpose The purpose of this paper is to investigate effects of layer thickness on densification, surface morphology, microstructure and mechanical and corrosion properties of 420 stainless steel fabricated by laser-powder bed fusion (L-PBF). Design/methodology/approach Standard specimens were printed at layer thickness of 10, 20 and 30 µm to characterize Archimedes density, surface roughness, tensile strength, elongation, hardness, microstructural phases and corrosion performance in the as-printed and heat-treated condition. Findings Archimedes density slightly increased from 7.67 ± 0.02 to 7.70 ± 0.02g/cm3 and notably decreased to 7.35 ± 0.05 g/cm3 as the layer thickness was changed from 20 µm to 10 and 30 µm, respectively. The sensitivity to layer thickness variation was also evident in properties, the ultimate tensile strength of as-printed parts increased from 1050 ± 25 MPa to 1130 ± 35 MPa and decreased to 760 ± 35 MPa, elongation increased from 2.5 ± 0.2% to 2.8 ± 0.3% and decreased to 1.5 ± 0.2, and hardness increased from 55 ± 1 HRC to 57 ± 1 HRC and decreased to 51 ± 1 HRC, respectively. Following heat treatment, the ultimate tensile strength and elongation improved but the general trends of effects of layer thickness remained the same. Practical implications Properties obtained by L-PBF are superior to reported properties of 420 stainless steel fabricated by metal injection molding and comparable to wrought properties. Originality/value This study successfully the sensitivity of mechanical and corrosion properties of the as-printed and heat-treated parts to not only physical density but also microstructure (martensite content and tempering), as a result of changing the layer thickness. This manuscript also demonstrates porosity evolution as a combination of reduced energy flux and lower packing density for parts processed at an increasing layer thickness.

Camera signal dependencies within coaxial melt pool monitoring in laser powder bed fusion

2020 ◽  
Vol 26 (1) ◽  
pp. 100-106 ◽  
Author(s):  
Tobias Kolb ◽  
Reza Elahi ◽  
Jan Seeger ◽  
Mathews Soris ◽  
Christian Scheitler ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Layer Thickness ◽  
Powder Layer ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Content Type ◽  
Powder Bed ◽  
Sensory Signals ◽  
Melt Pool ◽  
Research Activities

Purpose The purpose of this paper is to analyse the signal dependency of the camera-based coaxial monitoring system QMMeltpool 3D (Concept Laser GmbH, Lichtenfels, Germany) for laser powder bed fusion (LPBF) under the variation of process parameters, position, direction and layer thickness to determine the capability of the system. Because such and similar monitoring systems are designed and presented for quality assurance in series production, it is important to present the dominant signal influences and limitations. Design/methodology/approach Hardware of the commercially available coaxial monitoring QMMeltpool 3D is used to investigate the thermal emission of the interaction zone during LPBF. The raw images of the camera are analysed by means of image processing to bypass the software of QMMeltpool 3D and to gain a high level of signal understanding. Laser power, scan speed, laser spot diameter and powder layer thickness were varied for single-melt tracks to determine the influence of a parameter variation on the measured sensory signals. The effects of the scan direction and position were also analysed in detail. The influence of surface roughness on the detected sensory signals was simulated by a machined substrate plate. Findings Parameter variations are confirmed to be detectable. Because of strong directional and positional dependencies of the melt-pool monitoring signal a calibration algorithm is necessary. A decreasing signal is detected for increasing layer thickness. Surface roughness is identified as a dominating factor with major influence on the melt-pool monitoring signal exceeding other process flaws. Research limitations/implications This work was performed with the hardware of a commercially available QMMeltpool 3D system of an LPBF machine M2 of the company Concept Laser GmbH. The results are relevant for all melt-pool monitoring research activities connected to LPBF, as well as for end users and serial production. Originality/value Surface roughness has not yet been revealed as being one of the most important origins for signal deviations in coaxial melt-pool monitoring. To the best of the authors’ knowledge, the direct comparison of influences because of parameters and environment has not been published to this extent. The detection, evaluation and remelting of surface roughness constitute a plausible workflow for closed-loop control in LPBF.

Experimental and numerical investigation on the effect of layer thickness during laser powder-bed fusion of stainless steel 17-4PH

2020 ◽  
Vol 9 (2/3) ◽  
pp. 1
Author(s):  
Ehsan Toyserkani ◽  
Adhitan Rani Kasinathan ◽  
Shahriar Imani Shahabad ◽  
Yuze Huang ◽  
Yahya Mahmoodkhani ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Numerical Investigation ◽  
Layer Thickness ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed

scholarly journals Effect of process parameters on the formation of single track in pulsed laser powder bed fusion

2019 ◽  
Vol 36 ◽  
pp. 176-183
Author(s):  
Ville Laitinen ◽  
Heidi Piili ◽  
Patricia Nyamekye ◽  
Kari Ullakko ◽  
Antti Salminen
Keyword(s):  
Process Parameters ◽  
Pulsed Laser ◽  
Powder Bed Fusion ◽  
Single Track ◽  
Laser Powder Bed Fusion ◽  
Powder Bed

Experimental and numerical investigation on the effect of layer thickness during laser powder-bed fusion of stainless steel 17-4PH

2020 ◽  
Vol 9 (2/3) ◽  
pp. 212
Author(s):  
Zhidong Zhang ◽  
Usman Ali ◽  
Yahya Mahmoodkhani ◽  
Yuze Huang ◽  
Shahriar Imani Shahabad ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Numerical Investigation ◽  
Layer Thickness ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed

scholarly journals Increasing the Productivity of Laser Powder Bed Fusion for Stainless Steel 316L through Increased Layer Thickness

2020 ◽  
Author(s):  
Alexander Leicht ◽  
Marie Fischer ◽  
Uta Klement ◽  
Lars Nyborg ◽  
Eduard Hryha
Keyword(s):  
Stainless Steel ◽  
Layer Thickness ◽  
Electron Backscatter Diffraction ◽  
Powder Layer ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Stainless Steel 316L ◽  
Powder Bed ◽  
Backscatter Diffraction ◽  
Am Processes

AbstractAdditive manufacturing (AM) is able to generate parts of a quality comparable to those produced through conventional manufacturing, but most of the AM processes are associated with low build speeds, which reduce the overall productivity. This paper evaluates how increasing the powder layer thickness from 20 µm to 80 µm affects the build speed, microstructure and mechanical properties of stainless steel 316L parts that are produced using laser powder bed fusion. A detailed microstructure characterization was performed using scanning electron microscopy, electron backscatter diffraction, and x-ray powder diffraction in conjunction with tensile testing. The results suggest that parts can be fabricated four times faster with tensile strengths comparable to those obtained using standard process parameters. In either case, nominal relative density of > 99.9% is obtained but with the 80 µm layer thickness presenting some lack of fusion defects, which resulted in a reduced elongation to fracture. Still, acceptable yield strength and ultimate tensile strength values of 464 MPa and 605 MPa were obtained, and the average elongation to fracture was 44%, indicating that desirable properties can be achieved.

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